Standards for Wireless Local Area Network (WLAN) technology have been developed as Institute of Electrical and Electronics Engineers (IEEE) 802.11 specifications. IEEE 802.11a and 802.11b use an unlicensed band at 2.4 GHz or 5 GHz. IEEE 802.11b provides a transmission rate of 11 Mbps and IEEE 802.11a provides a transmission rate of 54 Mbps. IEEE 802.11g applies Orthogonal Frequency-Division Multiplexing (OFDM) at 2.4 GHz to provide a transmission rate of 54 Mbps. IEEE 802.11n may use Multiple Input Multiple Output (MIMO)-OFDM, and provide a transmission rate of 300 Mbps to four spatial streams. IEEE 802.11n may support a channel bandwidth up to 40 MHz to provide a transmission rate of 600 Mbps.
IEEE 802.11ai which is a new standard for supporting fast initial link setup of IEEE 802.11 stations (STAs) through an IEEE 802.11 Medium Access Control (MAC) layer has been developed. IEEE 802.11ai is intended to provide a technology for supporting link setup at a high speed in a state that huge users simultaneously access a new WLAN by leaving a wireless LAN coverage which is typically accessed by them in case of transfer of public transportation. Also, main features of IEEE 802.11ai are security framework, IP address assignment, and fast network discovery.
Also, in a 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) or LTE-Advanced (LTE-A) system, a user equipment (UE) may perform a random access process to acquire an uplink transmission timing alignment value or perform other various purposes. For example, if the user equipment transmits a random access preamble to a base station, the base station may provide a random access response to the base station in response to the random access preamble.